Inclusion complexes of chlorzoxazone with β- and hydroxypropyl-β-cyclodextrin: Characterization, dissolution, and cytotoxicity
Introduction
Chlorzoxazone (CZX, Fig. 1a) is a synthetic drug with various pharmacological actions. This drug is regularly used as a central nervous system-acting muscle relaxant to treat muscle spasms (Attia, Ramsis, Khalil, & Hashem, 2012) and provide pain relief. CZX has been proven to present certain curative effects on systemic mastocytosis, conjunctivitis, and ulcerative colitis (Gnanasambandan, Gunasekaran, & Seshadri, 2014); it can also be used to treat children's mental dysplasia caused by central nervous system lesions. Several researchers have reported a number of CZX applications (Feil et al., 2013, Hopf et al., 2011, Shaik and Mehvar, 2011).
Despite the many benefits of the drug, the biomedical applications of CZX are still limited by its disadvantages, which include low water solubility and high toxicity. Due to its poor water solublility, oral solid preparation has been the main form of CZX in clinical application. Thus, to improve the solubility and dissolution of CZX is a problem requiring to be solved urgently. Previous studies reported use solid dispersion technique or cosolvents solubilization method to enhance the solubility or dissolution of CZX (Chen and Frank, 1983, Swati et al., 2013). However, the dissolution of the product still has great room for improvement.
High toxicity of CZX is the other limitation for clinical application. Clinical studies have shown that CZX exhibits a particular degree of liver toxicity after it was applied with a combination of acetaminophen (Parafon Forte) for several months, and two deaths involving hepatic failure have been reported (Powers, Cattau, & Zimmerman, 1986). Thus, in view of the above shortcomings, to employ other methods to increase water solubility and dissolution rate, and decrease toxicity of CZX is a crucial and meaningful endeavor.
Cyclodextrin (CD) complexation technology has often proved to be the most successful in improving the solubility and dissolution of poorly soluble drug. CDs (Fig. 1b) generally possess a truncated conical shape as well as structures with a hydrophobic cavity, hydrophilic ends, and an external region. They present important functions in the field of supramolecular chemistry because several types of guest molecules may be accommodated by the CD cavity (Delvalle, 2004, Saenger, 1980, Szejtli, 1998). In particular, CDs are believed to enhance the physicochemical and pharmacodynamic properties, including stability, solubility, dissolution rate, and drug bioavailability, of their guest molecules (Bekers et al., 1991, Duchene and Wouessidjewe, 1990). To the best of our knowledge, no scientific study about the effect of CDs on increasing the solubility and dissolution rates of CZX has yet been published.
This work aimed to improve the water solubility and reduce the toxicity of CZX via complexation with β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD, Fig. 1b). Firstly, drug/CD interactions in solution were investigated by phase solubility studies, the solid complexes were prepared and characterized by Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), 1H nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). In addition, molecular models of the two complexes were calculated to verify the geometrical configurations of the complexes from experimental results. Moreover, to investigate the possible dissolution properties of the complexes in the stomach and intestine, pure water and aqueous solutions of pH 1.2 and 6.8 were used as dissolution media in dissolution tests. Finally, the inhibitory effects of free CZX and the complexes on liver LO2 cell growth were also investigated to evaluate decreases in the toxicity of CZX. The CD inclusion complexes exhibit great potential for future biomedical applications.
Section snippets
Materials
CZX (purity > 99%), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), and dimethyl sulfoxide (DMSO) were purchased from Sigma–Aldrich Co., LLC. (Shanghai, China). HP-β-CD and β-CD (BR purity > 99%) were obtained from Chengdu Kelong Chemical Co., Ltd. (Chengdu, China). The human liver cell line LO2 was purchased from the American Type Culture Collection (Manassas, VA, USA). Other reagents and chemicals used were of analytical reagent grade. Tri-distilled water was used throughout
Synthesis of the inclusion complex
The solid products were washed twice using methanol and triple-distilled water to remove free CZX and CDs. Afterward, the purified samples were dried and weighed. β-CD and HP-β-CD inclusion complex yields of 76.27% and 78.85%, respectively, were obtained.
Phase solubility studies
Phase solubility studies are widely used to study the solubility of drugs in the presence of CDs. The phase solubility behaviors of CZX in aqueous solutions of β-CD and HP-β-CD alone at 295, 300, 305, and 310 K were determined and relevant
Conclusions
In the present work, CZX–CD complexes with excellent water solubility and low toxicity were successfully prepared. The FT-IR, PXRD, DSC, 1H NMR, and SEM results confirmed the formation of the β-CD–CZX and HP-β-CD–CZX inclusion complexes. The high KC values obtained suggest that the inclusion complexes formed between CZX and CDs are quite stable. Molecular modeling studies revealed that the aromatic nucleus of CZX is entirely embedded into the CD cavities. The HP-β-CD–CZX complex showed better
Acknowledgements
This work was supported by the Applied Basic Research Project of Sichuan Province (Grant No. 2014JY0042), the Testing Platform Construction of Technology Achievement Transform of Sichuan Province (Grant No. 13CGPT0049), and the National Development and Reform Commission and Education of China (Grant No. 2014BW011). We thank the College of Polymer Science and Engineering, Sichuan University, for providing instrumentation and infrastructure for the thermal and morphology analysis.
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